The aims of this project are to explore the nature of the breakdown in the spatiotemporal organization associated with communicative disorders. To accomplish this task, many of the experiments are based on hypotheses about normal speech motor control and sensorimotor organization. The techniques employ parallel monitoring at all accessible levels of measurement; e.g., muscle activity by electromyography, movement by optoelelectric tracking, and speech acoustic analysis. The studies of the speech of stutterers will examine and compare spatiotemporal coordination in fluent and dysfluent speech, the modification in speech motor control as a function of therapy in developing and adult stutterers, and computational modeling of fluent and dysfluent speech. Experiments on the speech of the hearing-impaired will focus on the temporal organization and developmental characteristics of speech motor control. These studies will provide useful theoretical and clinically relevant information and procedures to assist in the understanding of these disorders, and will critically evaluate behavioral changes associated with specific therapy management programs. Finally, the results of these experiments should extend our understanding of normal speech production, in that a complete model should be able to account for normal and disordered speech output. The clinical subjects examined in this section are chosen because the speech disruption does not occur as a result of muscle impairment or structure abnormality, but rather, involves the control process itself.